Repetitive Nerve Stimulation Test Can Be Useful Diagnostic Tool in MG Crisis, Study Finds

Joana Carvalho, PhD avatar

by Joana Carvalho, PhD |

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MG and multiple myeloma

repetitive nerve stimulation test can be a fast and accurate diagnostic tool for myasthenia gravis patients undergoing a myasthenic crisis.

The study, “Repetitive Nerve Stimulation Test in Myasthenic Crisis,” was published in Muscle & Nerve.

Myasthenia gravis (MG) is an autoimmune disorder that affects the muscles’ ability to contract, leading to muscle weakness and extreme fatigue. During its early stages, MG tends to affect only one group of muscles. But in later stages, patients might start to lose respiratory muscle control and have difficulty speaking, chewing, or swallowing.

This can lead to a myasthenic crisis, a serious complication that usually requires hospitalization and respiratory support.

“Because of the critical nature of myasthenia gravis crisis, it is essential for the clinicians to diagnose MG quickly in new onset MG crisis patients and confirm MG crisis in known MG patients who present with atypical clinical features,” the researchers said.

The repetitive nerve stimulation (RNS) test is a conventional diagnosis tool for MG that was implemented in the 1970s. During the test, physicians place electrodes on a patient’s skin over the muscles they wish to test. The electrodes send small electrical pulses that allow doctors to measure the nerve’s ability to send these signals to the muscle tissue. If signal transmission worsens with muscle fatigue, the patient is diagnosed with MG.

Although the RNS test is considered an accurate and fast diagnostic tool for MG, studies evaluating its usefulness during a myasthenic crisis are rare.

In this study, researchers from the University of Alabama reported the outcomes of the RNS test in a group of patients undergoing a myasthenic crisis.

The retrospective study analyzed the medical records of 26 patients who underwent the RNS test while having a myasthenic crisis between 1997 and 2017.

In 18 patients (69%), the myasthenic crisis was considered the first manifestation of the disease. In this group of patients, 17 (94%) were diagnosed with MG based on an abnormal result of the RNS test. In the remaining eight patients with known MG, the RNS test identified six (75%) who were undergoing a myasthenic crisis.

Moreover, researchers found three different patterns of abnormal RNS tests: the classic MG pattern in 24 (92%) patients; the Lambert-Eaton myasthenic syndrome (LEMS) in one patient; and the cholinergic crisis pattern in one patient.

“From this, we conclude that, during the MG crisis, the RNS test can provide a rapid and sensitive diagnostic test for MG in the majority of patients,” the investigators concluded.